A so-called I-beam, named because of its resemblance in section to the capital letter I, is a well-known type of load-bearing member used in many applications (e.g., construction of buildings). In the usual case, and considering that the type of material used has been previously decided upon, in order to obtain a stronger I-beam or one having a greater load bearing capacity, the various parts of the I-beam have been merely increased in size which, unfortunately, also increases the weight of the beam. Alternatively, there has been the known option of using a material having a higher modulus of elasticity. However, in the usual case a material that is inherently stronger will also be more costly and may possess other physical characteristics that are not desirable. As a result of all this, in the past when it was desired to increase the load-bearing properties of an I-beam this necessitated either an increase in beam weight, the cost, or both.
A standard process for making I-beams has been to heat a billet of rectangular cross-section to an elevated temperature and engage it with forming rolls which shape the billet to the desired configuration. In this way, the I-beam flanges and web are formed at the same time. Although hot-rolled I-beams are excellent for many uses (e.g., railroad tracks) especially where very high bearing stresses are contemplated, they are relatively expensive and complex to manufacture.
Another process for manufacturing an I-beam is to assemble individual flanges and web together by edge welding the web to the flanges. Such a construction is less expensive than the hot-roll method. Welded I-beams are widely accepted and have found extensive use in the building construction industry. For example, welded beams are almost exclusively used in the construction of so-called mobile homes.
However, conventional welded I-beams have not been found to be completely satisfactory in that under certain high-load conditions the typical rectangular shaped webs have exhibited the tendency to buckle or deform permanently about a longitudinal axis (i.e., failing in bearing stress).
Still further, it is advisable under some circumstances to be able to pre-camber an I-beam (i.e., provide with unstressed curvature about a transverse axis) and this is a difficult undertaking with the usual rectangular shaped platelike web.